Heybeliada or Heybeli Ada is the second largest of the Prince Islands in the Sea of Marmara, near Istanbul. It is officially a neighborhood in the Adalar district of Istanbul, Turkey.
The large Naval Cadet School overlooks the jetty to the left as you get off the ferry or seabus. There are two interesting pieces of architecture on the grounds of the school. One is Kamariotissa, the only remaining Byzantine church on the island, and more importantly the last church to be built before the conquest of Constantinople. The other is the grave of Edward Barton, the second English Ambassador to be sent to Constantinople by Elizabeth I of England, who spent his last days in Heybeli in order to escape the plague raging through the city in 1598. His remains were later relocated to the British Cemetery in the Haydarpaşa quarter of the Üsküdar district.
Please check the ferry timetables on the websites.
Ticket of the regular ferry to the Princes' Islands: 3.50 TL with IstanbulCard, 5 TL with token
Fast ferry tickets: from Kabataş (European side): 7.10 TL with IstanbulCard, 9 TL with token
From Bostancı (Asian side): 4.25 TL with IstanbulCard, 5.50 TL with token
Wikipedia https://en.wikipedia.org/wiki/Heybeliada
Ferry Timetable http://en.sehirhatlari.istanbul/en/timetable/besiktas-heybeliada-buyukada-3487.html
Coordinates 40°52'30.72" N 29°5'24.76" E